In recent years, new forms of lighting including low-voltage halogen lamps and gas discharge lamps such as compact fluorescent and high intensity discharge lamps (or HID lamps including metal-halide and sodium lamps) have become increasingly popular owing to their superior efficiency and light color. Unlike conventional incandescent lamps which can be powered directly from the 120V/60 Hz or 230V/50 Hz utility power, these lamps require power supplies. Specifically, low-voltage halogen lamps require a transformer to provide a voltage typically equal to 12V and gas-discharge lamps require an ignition mechanism and a ballast to control the currents running through them.
With the increased popularity of these types of lamps, it is becoming increasingly important to find economical and aesthetic ways of providing for their power needs. It is also desirable to provide more versatile power supply systems which allow consumers to mix different types of lamps together economically and aesthetically, in a manner not hitherto allowed for.
In this context it is important to note that all known approaches to powering modem lamps involve having a single power supply for each lamp (with the limited exception that identical low-voltage halogen lamps can be connected in parallel to a single transformer in an arrangement known as a low-voltage lighting track) such arrangement necessarily being costly and anaesthetic in that individual power supplies are bulky and expensive.
It is known in the art that the transformer for a low-voltage lamp may be replaced by a small ferrite based transformer if the input voltage passes through an electronic inverter which produces a square-wave voltage of high frequency, typically about 30 KHz
It is also known that a ballast for a gas discharge lamp, in which the central component is typically an inductance, can be made smaller by using electronic circuits switching at a high frequency again typically of the order of 30 KHz.
In particular, the approach of inverting 50 Hz or 60 Hz utility power to give high frequency current of 30 KHz modulated at 50 Hz or 60 Hz has been thought inapplicable to HID lamps because the arc in the HID lamps is likely to extinguish at the zero-crossing of the envelope due to the fact that the amplitude of the high frequency alternating voltage becomes very low for a number of milliseconds. Thus, there us up to now been no practical way to unify any elements of the power supplies for halogen and HID even had the concept of a central unit with some common elements been conceives
In addition to the apparent lack of compatibility of the approaches to miniaturizing power supplies for halogen and HID, the use of high frequency for even systems of one type of lamp is subject to a drawback: namely that the square wave 30 KHz used in power supplies for lighting necessarily contains strong harmonics of much higher frequencies than 30 KHz. When the power supply is not adjacent to the lamp, the wires connecting the two act as a transmission line emitting electromagnetic radiation which can interfere with surrounding equipment and which may violate European, FCC or equivalent standards for electromagnetic compatibility. Clearly this drawback becomes far more serious as the power is increased and as the illumination system extends over larger distances. In practice, this places a limitation on the number of lamps which may be connected simultaneously to the system
A low-voltage lighting track operating at 12V is known which is specifically designed for low-voltage halogen lights and which is sometimes powered by a so-called electronic transformer which includes a central inverter in combination with a central transformer. Such a system suffers from the problem described above and this is generally overcome by limiting the length of the system, particularly in Europe, to about two meters, and by limiting the current to about 20 amps or 25 amps, so as to limit the magnitude of the electromagnetic radiation emanating from the system. Clearly, this system cannot be used with lamps other than low voltage lamps.